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Carbon-Carbon Bond Forming Reactions of Metal-Bonded Hydrocarbon Groups on Ag(111): Steric, Electronic, and Carbon Hybridization Effects on the Coupling RatesLee, Long-chen 06 August 2006 (has links)
The alkyl substitution effects and the hybridization effects on the rate of coupling of adsorbed hydrocarbon groups on Ag(111) have been investigated under ultrahigh vacuum by temperature programmed reaction/desorption (TPR/D). For these two different issues, two types of halide precursors were used. One is to form adsorbed fragments bearing C£\(sp3) and C£\-H, the other is to yield adsorbed fragments with different hybridized £\-carbons without C£\-H. The desired hydrocarbon groups were generated on Ag(111) by the thermal dissociation of the C-X (X = I or Br) bond in the corresponding halogenated compounds. Substitution of alkyl for hydrogen in the adsorbed alkyl groups systematically raises the coupling temperature. For example, 3-pentyl groups homo-couple at temperatures ~ 70 K higher than the ethyl homo-coupling reaction. The concept of ¡§geminal repulsion¡¨ can account for our experimental results while the size and the number of the alkyl substitution groups increase. Different hybridized C£\ (metal-bonded carbon) species cause various angle strain energies in the cyclic transition state for the coupling reaction. The C£\(sp) species (CH3C¡ÝC(ad) and (CH3)3SiC¡ÝC(ad)) have rather high coupling temperatures (~ 460 K) due to the unidirectional sp orbital and the stronger Ag-C(sp) bond in the transition state. The relative rates for homo-coupling as a function of the hybridization of the metal-bound carbon follow the trend sp3 > sp2 > sp on the Ag(111) surface. Lastly, we found that the isobutyl groups undergo a £]-hydride elimination instead of homo-coupling on the Ag(111) surface. It may be due to that isobutyl groups have a total of nine £]-hydogens among all the hydrocarbon groups, which makes this rare reaction pathway possibly occur on Ag(111).
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In Situ Polarization Modulation Infrared Reflection Absorption Spectroscopic and Kinetic Investigations of Heterogeneous Catalytic ReactionsCai, Yun 14 January 2010 (has links)
A molecular-level understanding of a heterogeneous catalytic reaction is the key
goal of heterogeneous catalysis. A surface science approach enables the realization of
this goal. However, the working conditions (ultrahigh vacuum (UHV) conditions) of
traditional surface science techniques restrict the investigations of heterogeneous
catalysis system under industrial working conditions (atmospheric pressures).
Polarization Modulation Infrared Reflection-Absorption Spectroscopy (PM-IRAS) can
be operated in both UHV and atmospheric pressure conditions with a wide temperature
span while providing high resolution (4 cm-1 is used in this dissertation) spectra. In this
dissertation, PM-IRAS has been employed as a major technique to: 1) obtain both
electronic and chemical information of catalysts from UHV to elevated pressure
conditions; 2) explore reaction mechanisms by in situ monitoring surface species with
concurrent kinetic measurements.
In this dissertation, NO adsorption and dissociation on Rh(111) have been
studied. Our PM-IRAS spectra show a transition of NO adsorption on three-fold hollow
sites to atop sites occurs at low temperatures (<275 K). NO dissociation is found to account for this transition. The results indicated the dissociation of NO occurs well
below the temperature previously reported.
Characterizations of highly catalytically active Au films have also been carried
out. Electronic and chemical properties of (1 x 1)- and (1 x 3)-Au/TiOx/Mo(112) films
are investigated by PM-IRAS using CO as a probe molecule. The Au overlayers are
found to be electron-rich and to have significantly different electronic properties
compared with bulk Au. The exceptionally high catalytic activity of the Au bilayer
structure is related to its unique electronic properties.
CO oxidation reactions on Rh, Pd, and Pt single crystals are explored from low
CO pressures under steady-state conditions (less than 1 x 10-4 Torr) to high pressures
(0.01-10 Torr) at various gaseous reactant compositions. Surface CO species are probed
with in situ PM-IRAS to elucidate the surface phases under reaction conditions. These
experimental results are used to correlate reaction kinetics and surface reactant species.
It is evident that there is a continuum over the pressure range studied with respect to the
reaction mechanism. The most active phase has been shown to be an oxygen-dominant
surface. The formation of a subsurface oxygen layer is found to deactivate the reaction.
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Electronic Properties of Phthalocyanines Deposited on H-Si(111)Gorgoi, Mihaela 16 February 2007 (has links) (PDF)
Im Rahmen dieser Arbeit wurden vier Phthalocyanine untersucht: Metallfreies-Phthalocyanin (H2Pc), Kupferphthalocyanin (CuPc) und Fluor-substituiertes Phthalocyanin (F4CuPc und F16CuPc). Das Ziel dieser Arbeit ist die Charakterisierung der elektronischen und chemischen Eigenschaften der Grenzflächen zwischen diesen Molekülen und Silizium.
Die Moleküle wurden durch organische Molekularstrahldeposition (OMBD) im Ultrahochvakuum auf wasserstoffpassivierte Si(111)-Substrate aufgedampft. Oberflächensensitive Messmethoden wie Photoemissionsspektroskopie (PES), Bremsstrahlung Isochromaten Spektroskopie (BIS oder IPES - Inverse Photoemissionsspektroskopie) und Spektroskopie der Röntgen-Absorptions-Feinstruktur (NEXAFS – Near Edge X-Ray Absorption Fine Structure) wurden zur Charakterisierung eingesetzt. Um eine Zuordnung der verschiedenen Komponenten in PES und IPES zu ermöglichen, wurden Methoden der Dichtefunktionaltheorie zur theoretischen Berechnung eingesetzt.
Die Energieniveauanpassung an der Grenzfläche zwischen der organischen Schicht und der H-Si-Grenzfläche, sowie die Transportbandlücke von H2Pc, CuPc, F4CuPc und F16CuPc wurden mit Hilfe von PES und IPES bestimmt.
Die NEXAFS-Messungen ermöglichten eine genaue Bestimmung der Molekülorientierung relativ zum Substrat. Die Auswertung der Daten zeigte unterschiedliche Molekülorientierungen in dünnen und dicken Filmen. Diese Änderungen wurden mit dem bandverbiegungsähnlichen Verlauf der HOMO-und LUMO-Positionen in Verbindung gebracht. Zusätzlich zu diesem Verhalten wiesen die Grenzflächen auch einen Grenzflächendipol auf, welcher durch die unterschiedlichen Austrittsarbeiten der Kontaktmaterialien hervorgerufen wird. Der Einfluss des Grads der Flouridierung wird durch eine ähnlichen Zunahme der Elektronenaffinität (EA), der Austrittsarbeit (WF) und der Ionisierungsenergie (IE) bestätigt.
Die elektronischen Eigenschaften von Metall/organische-Schicht-Grenzflächen und von organischen Schichten unter Sauerstoffeinfluss wurden mit Hilfe von PES und IPES untersucht. Die Ag/Pc Grenzflächen zeigten eine Mischung aus HOMO-LUMO-Verschiebungen und Grenzflächendipolbildung. An den Ag/H2Pc- und Ag/F16CuPc- Grenzflächen wurde ein Ladungstransferkomplex gebildet. Auf der CuPc-Schicht physisorbiert das Ag lediglich und im Fall von F4CuPc wird Ladung zu Ag transferiert, wobei eine andauernde n-Typ-Dotierung an der Grenzfläche erzeugt wird. In Analogie zum Fall der Pc/H-Si Grenzfläche wiesen die Dipole, die hier gefunden wurden, eine lineare Abhängigkeit von EA, WF und IE auf und können durch die Differenz zwischen den Austrittsarbeiten vorausgesagt werden.
Das Verhalten der dicken organischen Schichten unter Sauerstoffeinfluss kann in zwei Gruppen eingeteilt werden. Eine Gruppe, bestehend aus H2Pc und F4CuPc, wies nur schwache Wechselwirkung auf und der Sauerstoff physisorbiert auf der Pc-Schicht. Die beiden anderen Moleküle, CuPc und F16CuPc konnten einer Gruppe starker Wechselwirkung zugeordnet werden. CuPc bildet einen Ladungstransferkomplex mit Sauerstoff und auf F16CuPc wird eine polarisierte Schicht gebildet. / In the context of this work four Phthalocyanine were studied: Metal-free Phthalocyanine (H2Pc), Copper Phthalocyanine (CuPc) and fluorine-substituted Phthalocyanine (F4CuPc and F16CuPc). The goal of this work is the electronic and chemical characteristics of the interfaces.
The molecules were deposited by organic molecular beam deposition (OMBD) in the ultra high vacuum on hydrogen-passivated Si(111)-Substrate. Surface sensitive techniques such as photoemission spectroscopy (PES), bremsstrahlung isochromate spectroscopy (BIS or IPES - inverse photoemission spectroscopy) and near edge X-ray absorption fine structure spectroscopy (NEXAFS) were used for characterisation. Theoretical computations by density functional theory methods were employed, in order to assign different components in PES and IPES.
The energy level alignment at the organic/H-Si interface, as well as the transport gap of H2Pc, CuPc, F4CuPc and F16CuPc were determined by PES and IPES.
The NEXAFS measurements determine the exact molecular orientation with respect to the substrate. The evaluation of the data showed different molecular orientation in the thin and thick films. This change was correlated with the band bending like behaviours that emerged at these interfaces. In addition to the band bending like behaviour, the interfaces show also an interface dipole which is driven by the work function difference between the contact materials. The influence of the degree of fluorination is confirmed in the similar increase of the EA, WF and IE.
The electronic properties of metal/organic layer interfaces and of organic layer under oxygen influence were examined by PES and IPES. The Ag/Pc interfaces show a mixture of HOMO-LUMO shifts and interface dipole formation. A charge transfer complex is formed in the case of Ag/H2Pc and Ag/F16CuPc interfaces. Ag is physisorbed atop the CuPc. Charge transfers from F4CuPc to Ag creating a continuous n-type doping at the interface. Similar to the Pc/H-Si interfaces the interface dipoles found here show a linear dependence on the EA, WF and IE and can be predicted by the difference in the work functions.
The data evaluation of oxygen exposed thick films determined two groups of behaviours. The weak interaction group is represented by H2Pc and F4CuPc, Pcs on which oxygen is physisorbed. The strong interaction group contains the other two molecules CuPc and F16CuPc. CuPc forms a charge transfer complex with oxygen and on top of F16CuPc a polarized layer is formed.
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Electrodéposition et la caractérisation de nanofilms palladium sur Au (111) pour le stockage d'hydrogène Electro-deposition and characterization of palladium nanofilms on Au (111) for hydrogen storageWang, Liang 21 December 2012 (has links) (PDF)
Ce travail de thèse s'est intéressé au dépôt électrochimique de filmsde palladium ultra-minces sur Au(111), à leur caractérisation et àl'insertion d'hydrogène dans ceux-ci. La caractérisation des nanofilmsen milieu sulfurique montre des signatures bien définies, qui évoluentavec l'épaisseur des dépôts. Nous avons pu attribuer à chaque pic uneréaction spécifique, en accord avec les mécanismes de croissancerévélés par les mesures SXRD in situ. La croissance pseudomorphede la 1ère couche se fait avec une première étape d'adsorption, suiviepar un mécanisme de nucléation et croissance. La croissance 3D de latroisième couche démarre avant la fin de la deuxième couchepseudomorphe.L'absorption d'hydrogène dans les nanofilms a été étudiée en milieusulfurique. L'isotherme d'insertion présente un élargissement dudomaine de la solution solide, un plateau avec une pente dans ledomaine bi-phasique et une diminution du taux maximal d'insertion del'hydrogène par rapport au Pd massif. Ce taux diminue avecl'épaisseur mai approche celui de Pd massif au déla delà de 15 MC.Deux éléments ont été considérés pour expliquer le comportement desisothermes: les deux premières couches pseudomorphes sontcontraintes par le support et des " tours " tridimensionnelles relaxéesse forment au delà de la 2ème couche.
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Etude par détection de photons des processus électroniques au sein d'une jonction tunnel dans un milieu moléculairePerronet, Karen 14 December 2004 (has links) (PDF)
La luminescence induite par STM (microscopie à effet tunnel) est une source d'informations d'une grande richesse sur les processus électroniques au sein d'un objet nanoscopique individuel. Nous nous sommes intéressés à une jonction Au/Au(111) sous vide puis dans un milieu moléculaire. L'étude sous vide a permis de montrer l'influence des variations spatiales des densités d'états de la surface. L'émission à l'interface liquide-solide a été démontrée et le rôle de la fonction diélectrique du solvant mis en évidence. Nous avons ensuite étudié les corrélations temporelles entre les photons émis. Selon le liquide environnant la jonction, les photons peuvent être émis par paquets. Nous relions ce phénomène à la modification structurelle de la jonction induite par la présence d'une molécule et à la différence d'énergie entre ses orbitales frontières. Si elle est assez faible, des chemins tunnel résonants existent et les électrons traversent la barrière par paquets. L'influence d'une couche auto-assemblée sur le substrat est étudiée. Des dérivés de triphénylènes interagissent trop faiblement avec Au(111), mais avec des alcanethiols chimisorbés, la résolution moléculaire est atteinte simultanément sur l'image STM et la carte de photons. Nous montrons que le contraste sur cette dernière provient de la modulation de l'extension spatiale à l'intérieur de la barrière des densités d'état locales due à la liaison S-Au. L'élaboration de multicouches organiques est alors envisagée pour observer l'électroluminescence d'une molécule unique, isolée du substrat par les thiols et étudier des corrélations d'origine électronique. Nous avons déjà caractérisé optiquement une telle couche de C60.
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Towards a Unifying Visualization OntologyVoigt, Martin, Polowinski, Jan 13 April 2011 (has links) (PDF)
Although many terminologies, taxonomies and also first ontologies for visualization have been suggested, there is still no unified and formal knowledge representation including the various fields of this interdisciplinary domain. We moved a step towards such an ontology by systematically reviewing existing models and classifications, identifying important fields and discussing inconsistently used terms. Finally, we specified an initial visualization ontology which can be used for both classification and synthesis of graphical representations. Our ontology can also serve the visualization community as a foundation to further formalize, align and unify its existing and future knowledge.
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Estudo de interações hiperfinas em compostos intermetálicos Gd(Ni, Pd, Cu)In, Tb(Ni, Pd)In, Dy(Ni, Pd)In e Ho(Ni, Pd)InLAPOLLI, ANDRE L. 09 October 2014 (has links)
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Ultra-thin oxide filmsHu, Xiao January 2016 (has links)
Oxide ultra-thin film surfaces have properties and structures that are significantly different from the terminations of the corresponding bulk crystals. For example, surface structures of epitaxial ultra-thin oxide films are highly influenced by the crystallinity and electronegativity of the metal substrates they grown on. Some enhanced properties of the novel reconstructions are related to catalysis, sensing and microelectronics, which has resulted in an increasing interest in this field. Ultra-thin TiO<sub>x</sub> films were grown on Au(111) substrates in this work. Two well-ordered structures within monolayer coverage - honeycomb (HC) and pinwheel - were generated and investigated. Special attention has been paid to the uniform (2 x 2) Ti<sub>2</sub>O<sub>3</sub> HC phase including its regular structure and imperfections such as domain boundaries (DBs) and point defects. Linear DBs with long-range repeating units have been observed; density functional theory (DFT) modelling has been used to simulate their atomic structures and calculate their formation energies. Rotational DBs/defects show up less frequently, however a six-fold symmetrical 'snowflake' DB loop stands out. Two types of point defects have been discovered and assigned to Ti vacancies and oxygen vacancies/hydroxyl groups. Their diffusion manners and pairing habits have been discussed within an experimental context. The results of growing NbO<sub>x</sub> ultra-thin films on Au(111) are also presented in this thesis. An identical looking (2 x 2) HC structure to the Ti<sub>2</sub>O<sub>3</sub> ultra-thin film has been formed; a stoichiometry of Nb2O3 is suggested. Another interesting reconstruction is a hollow triangle structure. Various sizes have been found, and sides of these equilateral triangles all show a double-line feature aligned along the { 1 ₁⁻ } directions of the Au(111) lattice. Chemical composition characterisations of NbO<sub>x</sub> thin films are still required as is DFT modelling. Experimental techniques used in this thesis include scanning tunnelling microscopy (STM), low energy electron diffraction (LEED), and X-ray photoelectron spectroscopy (XPS). Ultra-thin oxide films were created by physical vapour deposition (PVD) in ultra-high vacuum (UHV) systems.
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The Right to Health Care of Terminally Ill Inmates in South AfricaAlbertus, Chesne Joy January 2018 (has links)
Doctor Legum - LLD / In South Africa, prison authorities are not primarily concerned with the health of the prison population. This is evidenced by inter alia: the vast number of complaints regarding health care received by the Judicial Inspectorate of Correctional Centres; natural deaths in prisons reported annually; litigation regarding health care and treatment in prisons; and the notoriously poor conditions of detention which inevitably have a negative impact on prisoners' health. There is as a result a noticeable difference between state provided health care to the public and health care in prisons. This thesis is therefore aimed at unpacking what the right to health means in respect of terminally ill prisoners. This question has been overshadowed by issues regarding medical parole in South Africa and intermittently by calls for palliative care in prisons. Whilst these issues are relevant to their plight, there is a need to articulate the scope of the right to health of terminally ill prisoners. This is imperative as not all prisoners who are terminally ill are eligible for medical parole and there are instances where the granting of such parole may be impractical. An analysis of the right to health in relation to terminally ill prisoners will provide legal certainty as to the legal entitlements regarding health care for one of the most vulnerable groups in society. They will know what they may legally claim and what they cannot insist upon in terms of the law.
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Diretrizes reestruturadoras das licenciaturas no Brasil: reflexões sobre um currículo de transição do curso de Licenciatura em Física / Restructuring guidelines for undergraduate degrees in Brazil: reflections on a transition curriculum of undergraduate physics courseSantos, Tais Andrade dos 19 February 2018 (has links)
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Previous issue date: 2018-02-19 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Esta pesquisa de mestrado tem o objetivo de investigar o processo de reestruturação curricular de um curso de licenciatura em Física para o atendimento a Deliberação CEE nº 111/2012 e a preparação para a Resolução CNE/CP nº 02/2015. A pesquisa se mostra relevante não apenas para mapear as alterações na grade curricular do curso, de acordo com a legislação, mas principalmente por conhecer as concepções dos gestores, professores formadores e discentes. Esse estudo de caso foi delineado a partir da seguinte questão de pesquisa: “Quais as concepções de Docentes, Gestores e Discentes do curso de Licenciatura em Física sobre as contribuições das modificações curriculares para a formação dos futuros professores?” e com os seguintes objetivos específicos: Conhecer e analisar os documentos oficiais que propõem as modificações no currículo; construir um instrumento de análise argumentativa, por meio das categorias de Toulmin, para que possamos ter uma visão global dos prós e contras do novo currículo pela visão dos sujeitos; analisar/inferir as contribuições do novo currículo para a formação de professores (em relação ao currículo anterior), ou seja, refletir sobre o perfil dos alunos egressos do curso considerando também as mudanças que ocorreram com a nova reestruturação implantada para os alunos ingressos no ano de 2018. Os métodos técnico-instrumentais utilizados foram: análise estrutural de conteúdo material; revisão bibliográfica, análise de documentos, entrevista e questionários analisados através do referencial teórico metodológico de análise da argumentação dos sujeitos. Os referenciais teóricos metodológicos que fundamentaram a pesquisa foram o Padrão de Argumentação de Toumin (TAP) para as concepções dos sujeitos e para as relações de currículo propostos por Apple. Como principais resultados obtidos nesse trabalho temos que apesar do perfil formativo da legislação apontar para uma racionalidade prática com uma estreita relação entre a teoria e a prática, a concepção dos docentes sobre a formação inicial prioriza “saber o conteúdo da Física”, relacionando a prática docente na formação inicial apenas às disciplinas pedagógicas. O processo de reestruturação neste estudo de caso foi realizado de modo verticalizado, apesar de parecer um discurso repetitivo de verticalização na adequação do currículo, os gestores e docentes neste estudo de caso demonstraram que o processo foi realizado apenas para o cumprimento burocrático das deliberações, de modo que os docentes evitaram ao máximo passar pelo processo. Além da implantação da diretriz causar mudanças no estilo de ensino do professor formador, em relação às concepções dos discentes, docentes e dos gestores sobre a reestruturação do currículo; um dos traços mais marcantes é a dicotomia entre o saber dos conteúdos de Física e didática, essa dicotomia aparece na imposição da deliberação CEE nº 111/2012, que ao assegurar uma carga horária para as disciplinas pedagógica nas licenciaturas, causa na postura dos sujeitos o discurso de que a alteração é interessante à formação dos futuros professores, desde que não altere a carga horária das disciplinas de Física. Por fim como contribuições deste trabalho compreende-se que é imprescindível que os currículos devem ser reformulados não apenas por documentos legais, mas que o processo de reflexão da formação inicial docente deve ser contínuo e repensado pelos próprios professores formadores e gestores. / This master's research aims to investigate the process of curricular restructuring of a degree in Physics for compliance with CEE resolution 111/2012 and the preparation for CNE / CP Resolution 02/2015. The research is relevant not only to map the changes in the course curriculum of the course, according to the legislation, but mainly to know the conceptions of managers, teachers and students. This case study was delineated from the following research question: "What are the conceptions of Teachers, Managers and Students of the Licentiate in Physics course on the contributions of curricular modifications to the training of future teachers?" And with the following specific objectives : To know and to analyze the official documents that propose the modifications in the curriculum; to construct an instrument of argumentative analysis, through Toulmin's categories, so that we can have a global view of the pros and cons of the new curriculum by the subjects' view; to analyze / infer the contributions of the new curriculum for teacher training (in relation to the previous curriculum), that is, to reflect on the profile of the students who graduated from the course, also considering the changes that occurred with the new restructuring implemented for students in the year of 2018. The technical-instrumental methods used were: structural analysis of material content; bibliographic review, document analysis, interview and questionnaires analyzed through the theoretical methodological reference of the analysis of the subjects' arguments. The theoretical methodological references that supported the research were the Toulmin Argumentation Standard (TAP) for the subjects' conceptions and for the curriculum relations proposed by Apple. As the main results obtained in this work we have that although the training profile of the legislation points to a practical rationality with a close relationship between theory and practice, the teachers' conception about initial training prioritizes “to know the content of Physics”, relating the teaching practice in the initial training only to the pedagogical disciplines. The restructuring process in this case study was carried out vertically, although it seems to be a repetitive discourse of verticalisation in the adequacy of the curriculum, the managers and teachers in this case study demonstrated that the process was carried out only for the bureaucratic fulfillment of the deliberations, of so that teachers avoided the process as much as possible. In addition to the implementation of the directive cause changes in the teaching style of the teacher trainer, in relation to the conceptions of the students, teachers and managers on the restructuring of the curriculum; one of the most striking features is the dichotomy between the knowledge of the contents of Physics and didactics, this dichotomy appears in the imposition of the CEE resolution No. 111/2012, which, by securing an hourly load for the pedagogical disciplines in the degrees, discourse that the change is interesting to the training of future teachers, as long as it does not change the workload of the Physics disciplines. Finally, as contributions of this work it is understood that it is imperative that curricula must be reformulated not only by legal documents, but that the process of reflection of initial teacher education must be continuous and rethought by the teacher trainers themselves and managers.
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